Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $183.75   8.304%   $199.0086   $199.01   $199.00   $199.00  
  Purchase #2 $152.99   5.646%   $161.6278   $161.63   $161.65   $161.60  
  Purchase #3 $26.31   13.268%   $29.8008   $29.80   $29.80   $29.80  
  Purchase #4 $98.81   13.529%   $112.178   $112.18   $112.20   $112.20  
  Purchase #5 $222.73   9.236%   $243.3013   $243.30   $243.30   $243.30  
  Purchase #6 $20.99   3.612%   $21.7482   $21.75   $21.75   $21.70  
  Purchase #7 $238.28   3.622%   $246.9105   $246.91   $246.90   $246.90  
  7 purchase totals = $943.86       $1,014.5752   $1,014.58   $1,014.60   $1,014.50